The present invention relates to an apparatus for controlling an internal combustion engine and, more particularly, to an apparatus for controlling the operation of an internal combustion engine when it is impossible to sense whether the throttle valve is open or closed.
Conventional apparatus for controlling the internal combustion engine of vehicle have detected the state of the engine by way of various sensors and switches installed in the engine. According to the state detected, the apparatus have provided control of fuel injection, ignition timing, idling speed of engine, and so on.
One of the switches installed in an internal combustion engine to detect the state of operation of the engine is an idle switch which, when the throttle valve is fully closed, is turned on or actuated to produce a signal indicating the full closure of the throttle valve. This signal from the idle switch is used to control the engine, especially at idle and deceleration.
For example, when the vehicle is decelerating, a misfire tends to cause emission of unburned harmful exhaust gas and a deterioration in the fuel economy. In an attempt to eliminate these problems, a method of controlling the fuel injection has been proposed in Japanese Patent Publication Laid-Open No. 74625/1978. Specifically, this method is to shut off the supply of fuel into the engine when the idle switch is actuated and the engine speed is in excess of a certain value.
On the other hand, when the vehicle is accelerated from rest condition where the throttle valve is kept closed, a transient delay in fuel supply tends to occur. This can be compensated for by a known control method. In particular, when the idle switch is turned off in response to opening of the throttle valve, fuel is injected not synchronously with the rotation of the engine, but independently of normal fuel injection synchronized to the rotation of the engine. It is also known to control the engine speed at idle in the manner described below. First, when the following conditions are satisfied: (1) the idle switch is actuated because of closure of the throttle valve; (2) the engine speed is below a certain value; and (3) the transmission is in its neutral position, the engine is regarded as idling. The engine speed at this time is feedback controlled to approach an intended value by controlling valves which control the amount of intake air or the amount of air-fuel mixture, using feedback technique.
As described above, the idle switch is used for various controls of the engine. If the output signal from the idle switch is at fault, i.e., if the switch malfunctions, making it impossible to sense the opening or closure of the throttle valve, then the idle switch is assumed to be turned off. At this time, the supply of a certain amount of fuel is assured to allow the vehicle to be driven to a repair shop or other safe place. If the idle switch is assumed to be turned on or actuated upon malfunction, i.e., if the above-described fail-safe system is not established, the idle switch is assumed to be turned on even when the throttle valve is open. Accordingly, if the engine speed exceeded a certain value, then the supply of fuel to the engine would be cut off by the mechanism described above. As a result, the engine would come to a stall. Hence, it would be impossible to drive the vehicle to a turnout or repair shop.
When the idle switch malfunctions, if the switch is assumed turned off as mentioned previously, a problem takes place. Specifically, when the throttle valve is actually fully closed, this state is not detected. Therefore, while the vehicle is driven to a repair shop, the above-described control operation which otherwise be carried out during the opening of the idle switch is not performed at all.
For example, when the fuel supply is to be controlled, even if the throttle valve is closed and the vehicle is decelerating, the fuel supply is not cut off but continues. Therefore, when the vehicle goes to a turnout or repair shop, a misfire causes emission of unburned exhaust gas. As a result, a large amount of harmful components, especially HC, is discharged into the atmosphere. In cases of vehicle having catalyst or reactor as exhaust gas cleaner, the heat load due to unburned exhaust gas increases.
Another problem arises in connection with the control over the speed of an idling engine. Specifically, the state of idle cannot be sensed and so the engine speed is not controlled by feedback technique. For example, the system forms an open-loop control system. If the suction or intake system is chocked with dust or the like, a sufficient amount of intake air or air-fuel mixture is not secured. This reduces the engine speed, creating the possibility of a stall. In the worst case, whenever the engine of the vehicle is driven to a repair shop falls into an idle, a stall takes place.
Accordingly, it is the object of the present invention to provide a control apparatus which is used for an internal combustion engine and which infers sufficiently accurately the opening or closure of a throttle valve from signals produced from other sensors installed in the engine, excluding the idle switch, that indicate the state of the engine, provided that the idle switch is at fault and that a normal signal is not produced from the idle switch, thereby enabling various controls of the engine at idle.